Nonpatent Document 1 discloses a configuration which includes a plurality of GPS (Global Positioning System) antennas, a plurality of GPS receivers respectively connected with the plurality of GPS antennas, an IMU sensor, and an integrated processing part.
The plurality of GPS antennas receive GPS signals which are transmitted from GPS satellites, and output them to the GPS receivers. The plurality of GPS antennas is comprised of a master GPS antenna and a plurality of slave GPS antennas. The master GPS antenna and the plurality of slave GPS antennas are mounted to a movable body so that distances between the master GPS antenna and the slave GPS antennas are lengthened as long as possible. This is because it is known that a state calculation value of the movable body can be detected with greater accuracy as the distances between the GPS antennas (base lengths) is longer. Here, the state calculation value of the movable body is an attitude angle of the movable body, for example.
The GPS receiver calculates and outputs a pseudo range, a Δ range, and a carrier phase of the received GPS signal. The IMU sensor includes an angular-velocity sensor and an acceleration sensor to measure and output an angular velocity and an acceleration of the movable body. The integrated processing part calculates a speed, an acceleration, and an attitude angle of the movable body based on the angular velocity and the acceleration from the IMU sensor. Here, the integrated processing part corrects errors of the calculated position, speed, and attitude angle using the pseudo ranges, the Δ ranges, and the carrier phases acquired from the plurality of GPS receivers.
Moreover, Nonpatent Document 2 discloses calculating double phase differences using four GNSS antennas, and calculating a position, a speed, and an attitude angle using the double phase differences. With this configuration, one GNSS antenna is set as a reference antenna among the four GNSS antennas to set a base line vector.